Increased lung vascular endothelial permeability induced by activation of polymorphonuclear leukocytes (PMNs) adherent to endothelial cells via ICAM-1 leads to protein-rich pulmonary edema formation and acute lung injury. However, the mechanisms responsible for PMN-induced increased endothelial permeability are incompletely understood. Our supporting data demonstrate that increased caveolae- mediated transcellular transport of albumin may contribute to increased endothelial permeability, and thus may be a factor leading to leaky lung microvessels. In this renewal application, we will address the role of PMNs in inducing the activation of caveolae-dependent transcytosis of albumin and promoting edema formation. The studies will test the hypotheses that (i) fMLP activation of PMNs stimulates caveolae- mediated albumin transcytosis in endothelial cells and mediates the increase in endothelial permeability and lung injury, and (ii) PMN activation of Src kinase in endothelial cells regulates eNOS-mediated NO production via PI3-kinase and Akt signaling and that the NO derived from PMN-endothelial interaction regulates transcellular and junctional permeability pathways to increase lung microvessel permeability. We will delineate the signaling pathways responsible for the activation of endothelial permeability and its consequences in the mechanism of lung edema formation. The approaches to be used include knockout mice, siRNA-induced suppression of protein expression, endothelial permeability assessment of transcellular and paracellular pathways, imaging analysis of caveolae mediated trafficking in live endothelial cells, and biochemical assessments of relevant signaling pathways. Studies in intact mouse lungs will be complemented by studies utilizing mouse lung endothelial cells to provide a more detailed and mechanistic understanding of the signaling basis of PMN-activated increase in endothelial permeability. These studies will provide a novel perspective into the mechanism of increased transendothelial permeability in lungs induced by PMN activation, with the hope of identifying novel molecular targets and better designing strategies directed at treating protein-rich pulmonary edemagenesis and acute lung injury. PROJECT NARRATIVE: Vascular injury and protein-rich pulmonary edema formation are life-threatening complications associated with inflammatory diseases such as ischemia/reperfusion injury and sepsis. We hypothesize that increased transendothelial albumin transport via a caveolar mechanism contributes to neutrophil-induced endothelial hyperpermeability during inflammation. This project therefore addresses the role of caveolae-mediated albumin uptake and transcytosis as compared to paracellular leakage of plasma protein in neutrophil-mediated increase in endothelial permeability and lung injury. We will assess the role of neutrophil activation of Src kinase in endothelial cells in regulating caveolin-1, dynamin-2, and eNOS function, and determine the consequences of increased albumin transport and NO production in regulating the transcellular and junctional permeability pathways.